Apparatus for fast-firing ceramic ware



March 7, 1961 H. H. GREGER 2,973,568

APPARATUS FOR FAST-FIRING CERAMIC WARE Filed Sept. 5, 1958 2Sheets-Sheet 1 ATTORNEY March 7, 1961 Filed Sept. 5, 1958 H. H. GREGER2,973,568

APPARATUS FOR FAST-PIRING CERAMIC WARE 2 Sheets-Sheet 2 A v INVENTOR'gigr- 1954MB ATTORNEY APPARATUS FOR FAST-FIRING CERAMIC WARE HerbertHans Greger, Glen Road, Rockville, Md.

vFiled Sept. 5, 1958, Ser. No. 759,307 6 Claims. (Cl. 25-132) settermaterials and shapes have become available, which i setter materialshave a sufciently longer life to enable use economically at the fasterrates of firing. In many instances, the ceramic material or ware itselfis capable of permitting several times the rate of ring that ispresently used, but in order to strike an economic balance betweenproduction of saleable ware and replacement cost for Setters, the firingschedule has been adjusted to the optimum cycle. The longer this cycle,the larger is usually the cross section and the length of the kiln andthe more ware it will hold, but also the initial investment andmaintenance costs will be larger the larger is the kiln. Conversely, thefaster the firing schedule, the smaller can be the cross section andlength of the kiln and the lower may be initial investment andmaintenance costs. Notwithstanding the differences in initial costs, thelife of a large conventional kiln and of a small fastre kiln constructedaccording to this invention, may be the same. Additionally, in thefast-tiring of ceramic tile great economies in the use of stain havebeen achieved. One-half of one percent of stain or less, instead of vepercent of stain being required in many instances Where translucencydevelops as a result of the fast rng.

The principal object of this invention is to provide an apparatus forfast-firing ceramic material and ware which will overcome thedisadvantages of tiring apparatus here,-

"tofore employed.

Still another object of this invention is to provide an apparatus forthe tiring of ceramic ware while said ware is supported on a bed of sandor other granular refractory material.

A further vobject of this invention is to replace the usual solidrefractory hearth in a ceramic iiringkiln by 'a bed of sand or othergranular refractory material.

Yet another object of this invention is to substitute rigid brickwork inthe movable member of a kiln by a bed of sand or other granularrefractory material.

A still further object of this invention is to provide a bed of granularrefractory material in a ring kiln not only for carrying the ceramicware to be fired but also as a source of granular particles for fusionto the ware providing same with a rough surface.

It is also an object of this invention to provide a kiln having arefractory hood mounted over a movable bed of hood and the body ofgranular material.

2,973,568 Patented Mar. 7," 1961 With these and other objects in viewwhich will appear from the following description, the invention residesin a kiln for fast-tiring ceramic material, and the parts andcombinations thereof.

In the drawings:

Figure l is a perspective view of a vfiring kiln constructed accordingto the present invention;

Figure 2 is a transverse sectional view taken on line 2-2 of Figure 1;

Figure 3 is a fragmentary vertical sectional view of the invention takenon line 3 3 of Figure l;

Figure 4 is an enlarged vertical sectional view, partially in fragment,taken on line 4-4 of Figure 3.

Referring to the drawings, a kiln 1G particularly suitable for carryingout the present invention comprises a substantially annular hood ormuifle 12 of inverted U- shaped cross section. The hood is fabricated ofrefrac tory heat-insulating material 14 encased in a shell 16 of sheetsteel or other suitable material. (See Figure 2;) The shell 16 extendsabout the upper and outer side Walls of the hood and extends partiallybeneath the bottom surfaces of hood 12 in the form of annular members 18of angular cross section. As shown in Figures 2 and 3, skirts 20 ofshell 16 are attached to shell annular members 18. These skirts protrudeinto a granular refractory bed 52.

As clearly shown in Figure 1, the hood 12 is supported through its shellby a framework 22 consisting of a plurality of columns 24 disposed aboutthe annular kiln and supporting a plurality of beams 26. With thisconstruction annular kiln 10 is suspended from the framework 22.Charging of ceramics, such as tiles 68, is by means of conveyor chute 13extending into the charging end of an annular tiring chamber 66.Discharge of ceramics 68 is by means of downwardly inclined bafedischarge chute 15, the friction between the ceramics and revolving sandbed 52 causing the latter to force the tiles onto lchute 1S.

The refractory portion of hood 12 is so profiled on its underside as toprovide annular firing chamber 66 through which ware to be tired iscarried. This annular firing chamber or muffle is surrounded byrefractory material 14 which confines the heat that causes the ware tobe matured. The refractory also carries burners or electric heatingelements 28, the latter being made either of resistance wire or ofsilicon carbide bars or the like. See Figures 2 and 3. In the event thatgas burners (not illustrated) are employed as heating elements burnerports could be cut in staggered relationship through the sides of hood12 and gas escape vents could be provided at the top of the hood.

The refractory annular hood 12 may be built of insulating brick or of aninsulating light-Weight castable. Such a castable couldbe cast in onepiece in place or in section blocks using suitable molds. The blocksthus produced are placed into shell 16 and, if accurate enough indimension, may not require cementing. By providing a groove l to 2inches deep in the outer parts of the seams between blocks, a tightpacking of asbestos may be provided for closing same. This conventionalfeature is not illustrated. This construction will provide the necessaryfree movement for heat expansion and for minimizing cracking on accountof it. Various castable refractory mixes for the blocks are availablecommercially which contain insulating grog or other insulatingmaterials, such as hollow alumina spheres, and it is desirable to usesuch substitutes.

Positioned beneath annular hood 12 is a turntable 30. See Figure 3.While various constructions may be employed for the turntable, forpurposes of the present invention turntable 30 is provided with acentral supporting base or pedestal 32, which is positioned on the ,theproximity of the particles to each other.

floor footing or other supporting surface. Turntable 30 is keyed tospindle 34. Spindle 34 rotatably bears in pedestal 32. Spindle 34carries large gear 36 which is driven by a pinion 3@ mounted on theoutput shaft 40 of a speed-reducing mechanism 42. The mechanism 42 isdriven by an electric motor or other suitable source. of power 44.

To reduce the load carried by spindle 34, turntable 30 is provided witha plurality of wheels 46. Wheels 46 are adapted toroll over circularendless track 48 positioned on the door or other supporting surface. Thewheels 46, by means of suitable axles, are rotatable in forks on theunderside of the turntable and are suitably distributed around thebottom of turntable 30.

Turntable 30 supports a pan 50 formed of steel or rother suitablematerial. In pan 50 a bed 52 of` granular material of a refractorycharacteristic such as sand is deposited. Bed 52 of sand or othersuitable granular refractory material is of a depth substantially equalto Y the depth of the pan S0. It will be noted that turntable 30 is ameans of supporting the bed of sand 52 and imparting to it rotary motionfor the purpose of moving supported articles through the tiring tunnel24 in hood 12 of the kiln.

While pan 5t) has been indicated in Figures 1 and 2 as being entirelyfilled with bed 52 of granular material, it is within the concept of thepresent invention to make the pan S0 of annular formation with respectto hood 12. YThis bed of granular material is of a circumferenceslightly greater than the circumference of hood 12. As an example, thegranular bed 52 shown in Figure 2 .may be contained by a pan of 9 feetin diameter and 12 inches in depth. This circular pan or trough is lledwith a granular material, such as bedding sand as is conven- `tionallyused in dinnerware fabrication and tiring.

There is no particular restriction as to the nature of this granularmaterial and its mesh size. For example, the sand or granular materialmay be quartz, calcined clay grog, alumina, mullite, kyanite, aplite,Zircon, zirconia, magnesia, and others. The size may vary between 14 to60 mesh for example. 'll'he composition and the size have to be chosen,however, inA a manner that the bed of sand or other granular materialremains free flowing. Essentially no sintering is permitted under thetemperature conditions in the kiln, insuring that profiling or levelingoperations of the bed surface may be conducted at all times withoutinterference. Such leveling operations are carried out automatically bya scraper 54, attached to the core of annular hood 12. In lieu ofscraper S4 rolls or similar devices, positioned at suitable points inthe path of travel of the bed, might be employed. Arcuate scraper 54- isshown in Figures l and 2.

The choice of the sand or granular material of the bed depends on thetop temperature ofthe tiring cycle land the interaction between the sandor granular material and the ware supported thereon. To explain, the twofactors are to some extent interrelated as increasing temperatures willpromote chemical reaction. The maturing range of a ceramic compositionmust be determined by tests. For example, if full density is desired,tests will indicate ranges between the lowest temperature at which thisdensity develops and the temperature where overring occurs, as shown bybloating, distortion, mechanical weakness, or even fusion of the edges.During these tests, several different sands or granular materials may betested for purposes of the bed. A good v idea as to just whatcomposition a sand or other granular ymaterial should have may beascertained quite readily, lsince those skilled in the art haveknowledge of the desired setting material for most ceramic compositions.

The tendency of a ceramic body to mature during kiln firing depends notonly on its composition, but also on the fineness of particle size inthe ceramic body and If the 4. Refractory B A particles are small, say0.5 to 1()` microns, and closely packed, they begin to interact,recrystallize, and grow at temperatures far below the sintering range ofa coarser composition, and strength of the ceramic body developsreadily. However, if the packing is loose and the particles are large,such as they would be in a supporting bed according to this invention,only some light cohesion of such coarse particles might develop. Suchcohesion is readily destroyed. This means that sand or other granularrefractory material in the bed can be used over a fairly wide range oftemperature. Precise ranges can hardly be given, but temperature andchemical reaction with the ware causing formation of a low-fusing slagare the most important criteria for the choice.

Silica sand with soft and hard porcelain may be used at temperatures upto cone 13 or up to about 1350" C. A similar limit of temperature mayapply to kaolin grog corresponding to a #l tire brick, kyanite orzircon. Sintered alumina, mullite, magnesia, and zirconia may be used attemperatures up 4to l550 C. under precautions previously outlined, oreven higher if the kiln is built for it.

If for some reason slagging problems in the refractory bed still exist,such as is the case with some rare earth compositions, then a specialparting material may be interposed between bed sand and ware. A preciousmetal foil, such as platinum, or even a thin zirconium oxide setterplate, can be used for such purposes.

Chart I The following are examples of ceramic compositions that may betired according to the present invention:

50-10 Grog 50%; Clay 50%.-.- up to Cone 20; up to odres, #l 1530'J C.Clays.

From reference to Figure 2 it will be noted that the refractory hood ormutile 12 is divided into four principal zones, the charging anddischarging zone 62, the preheating zone 56, the tiring zone 58, and thecooling zone 60. The charging and discharging zone 62 is kept relativelysmall in order to provide as much space as However, the chargintroducingthe sand through hopper 64 and leveling the bed surface between chargingand discharging.

The preheating and cooling zones S6 and 60 respectively are essentiallysimilar in profile and construction unless either fast cooling isrequired or less of the insulating refractory need be provided in thecooling zone. On the other hand, additional cooling may be provided foroutside of refractory hood 12. Additional preheating may be gainedwithin the space provided by mounting a fan (not illustrated) at thedischarge end of annular hood 12, said fan blowing heated air toward thecharging end and into pre-heating zone 56. The tiring zone 58 may havegas burner ports either on the side of the mule 12 or on its top.Corresponding gas vents for the waste gases are provided, for example,through the top if the burners are placed on the sides. When electricheating elements are used, they are placed through oversize holes in thesides of the hood near the top ot the muile. The tiring zone may occupy,for example, about one-third or more of the mutfle length.

A narrow space is provided between the bottom of the hood refractory andthe upper surface of the sand bed. In order to close this gap, skirts 20'areprovided which enter sand bed 52 and form a seal. These skirts areattached to the muie shell 16 and its inner annular member 18. Skirtplows (not illustrated) may be employed to urge a marginal ange 64 ofsand about skirt 20. See Figure 4, in this connection.

While it is important to have the hood and the sand bed in accurateposition with respect to each other, this accuracy of positioning is notnearly as important here as it would be if the sand were replaced byrigid refractory material. Accuracy of tolerance then required would befar beyond normal construction and operating techniques and would beconsiderably more costly. Free sand cannot readily jam, it is capable ofmovement upon either heat expansion, cracking of the refractory or othercauses, such as jamming of the ware. It is one of the importantfunctions of the sand bed to give or deform and to help adjust to suchabnormal conditions of operation. It is also an important function ofthesand bed to provide easy access to the interior of the kiln for repairs.

The kiln may be built for the manufacture of tile, dinnerware and otherWare capable of being fired rapidly. The characteristics of the sandwill, of course, have to be somewhat adjusted to the specific use. Inmost cases, for example, it will be necessary to select the bed sand forabrasion resistance, besides refractoriness, spalling resistance, andresistance to thermochemical reaction with the ware. In some instances,it may be desirable to cause adhesion by fusion of bed sand to theunderside of the tile to provide a rough bottom surface for cementingthe tile to a wall. In such instances, the tile may consist oftranslucent porcelain which upon heating becomes soft enough to fuse tothe sand. Tests have shown that such a tile body when it softens becomescompletely level and conforms substantially to the level surface of thesand bed.

By the proper choice of refractory sand and the body of the ware, alarge variety of fast-lire operations can be carried out. If a necessityarises, the sand bed may be changed freely and without large expense.Also cleaning of the sand bed byscreening or washing may occasionally benecessary. For better heat insulation, the lower portion of the pan maybe lled with such high quality insulating materials as diatomite blocksor the like. In order to compensate for expansion deviation in the pancarriage rollers 46 may be widened.

The successful fast-fire operation according to this invention dependsprimarily on heating and cooling of the ware without involving a largeamount of rigid refractory material in the form of Setters, kiln walls,and kiln car tops. Rigid refractory materials, on the other hand, andduring frequent heating and cooling, fatigue readily, crack, and spall.Also the less the mass which has to be heated, the lower is the fuelcost as in practice of the instant invention. The only large refractoryshapes are in the annular hood where they stay at relatively constanttemperature and are not subject to rapid heating and cooling whichaccompany cracking and spalling, Only when the kiln is placed into orout of operation does heating and cooling take place. In beginning orstopping operation rates of temperature change are relatively slow andreadily controlled.

Successful fast-tiring according to this invention also requires heatingthe pieces of ware almost individually, such as is possible in a singlelayer, and on a bed of sand. Such individual heating is largely thepurpose of the rotating sand bed kiln. The sand bed is not subject tocracking and spalling, it is a good and cheap heat insulator, and when acircular motion is arranged, it is a good conveyor.

The furnace of this invention contemplates the use of temperatures wheresteel or other metal will be rapidly destroyed (i.e. in excess of 950C., maximum for Ni-Cr alloy). All metal parts in this invention, it willbe noted, are located outside the heating zone and are protected byinsulation and cooled by air. They will not thus be subject todestruction. Having described my invention, I claim:

1. A kiln for fast ring ceramic ware at high temperature comprising anupright framework, an annular mu'le mounted in said framework and havingdownwardly extending skirts, a heat shock free kiln floor composed of ashell filled substantially with a homoge-A neous 14 to 60 meshlgranular,free-flowing refractory material being essentially free from sinteringat temperatures in excess of 950 centigrade, said kiln floor beingrotatably mounted with respect to said mufle so that said skirts of saidmuflie protrude into said lloor, and means for moving the floorrelatively to said muffle to advance ceramic material supported on saidoor through said mufile.

2. A kiln as in claim l, said granular refractory material beingmullite.

3. A kiln as in claim 1, said granular refractory material beingalumina.

4. A kiln as in claim 1, said granular refractory material beingzirconia.

5. A kiln as in claim l, said granular refractory material beingmagnesia.

6. A kiln for fast tiring ceramic ware at high temperature comprising anupright framework, an annular munie mounted in said framework and havingdownwardly extending skirts, a heat shock free kiln floor composed of ashell filled substantially with a homogeneous 14 to 60 mesh granular,free-owing refractory material being essentially free from sintering attemperatures in excess of 950 centigrade, said kiln floor beingrotatably mounted with respect to said mulile so that said skirts ofsaid muie protrude into said oor, means for moving the floor relativelyto said mule to advance ceramic material supported on said oor throughsaid mue, and means supported in said framework for adjusting the levelof said granular refractory material and for replenishing said granularrefractory material.

References Cited in the le of this patent UNITED STATES PATENTS 906,416Harkins Dec. 8, 1908 1,881,683 Knapp Oct. 11, 1932 2,188,608 Littletonet al. Jan. 30, 1940 FOREIGN PATENTS 45,706 Denmark May 11, 1932 740,254Germany Oct. 15, 1943

